Flexibility and intensity of global water use

Water stress is often evaluated by scarcity: the share of available water supply being consumed by humans. However, some consumptive uses of water are more or less flexible than others, depending on the costs or effects associated with their curtailment. Here, we estimate the share of global water consumption over the period 1980–2016 from the relatively inflexible demands of irrigating perennial crops, cooling thermal power plants, storing water in reservoirs and supplying basic water for humans and livestock. We then construct a water stress index that integrates the share of runoff being consumed (scarcity), the share of consumption in these inflexible categories (flexibility) and the historical variability of runoff weighted by storage capacity (variability), and use our index to evaluate the trends in water stress of global major river basins on six continents. We find that the 10% most stressed basins encompass ~19%, 19% and 35% of global population, thermal electricity generation and irrigated calorie production, respectively, and some of these basins also experience the largest increases in our identified stress indexes over the study period. Water consumption intensities (water used per unit of goods or service produced) vary by orders of magnitude across and within continents, with highly stressed basins in some cases characterized by high water consumption intensities. Our results thus point to targeted water mitigation opportunities (for example, relocating crops and switching cooling technologies) for highly stressed basins.